1. Field of the Invention
This invention is in the field of dry cleaning solvent recovery. More particularly, this invention relates to a device and process for recovering dry cleaning solvent while minimizing losses of solvent to waste and/or release of solvents to the environment.
2. Prior Art
Dry cleaning processes employ halohydrocarbon liquids such as perchloroethylene, tetrachloroethylene, trichlorofluoromethane, trichlorofluoroethylene or the like to remove a mixture of fatty acids, oils, oil-soluble and insoluble dirt and soil, water and body moisture, and water-soluble dirt and soil from garments and other fabric products. Commonly, the garment or other fabric is contacted with the halohydorcarbon solvent with agitation and the soiled solvent is continuously passed through a filter to isolate the various contaminants picked up by the solvent and return clean solvent to the contacting zone.
Two filtration processes are widely employed. One process uses fabric bag filters coated with filter aids such as diatomaceous earth, carbon black, surfactants, and the like, through which the soiled solvent is passed. The other common process employs disposable filter cartridges having paper or fiber filter elements and carbon.
With either filtration process, the pressure drop across the filter is monitored and when the pressure drop rises to a critical level, the filter is cleaned. This is carried out in the case of filter bags by backwashing and in the case of cartidges by replacement.
The filter bag backwash liquid contains substantial amounts of solvent and is commonly flashed to recover a substantial fraction of the solvent. Nevertheless, the solid residue which results from the flash of the backwash liquid often contains 40%, 50%, 60% or more of solvent. Similarly, the discarded filter cartridges contain large proportions of solvent.
Simple disposal of the solvent-laden residue or filters is not attractive. One problem is that the solvent is expensive and its regular discard in multigallon quantities can add up to a large cost. A more pressing problem is that halohydrocarbon cleaning solvent is considered environmentally hazardous, and its release into the atmosphere or into dump sites is being increasingly regulated. One cannot freely discard such wastes but should treat them as hazardous substances.
Devices have been proposed heretofore for reducing the solvent content of used filters. These devices have been self-contained systems which employ jets of steam to strip out solvent. These devices condense the outflow to give a liquid product. These devices offer the advantage of speed, but are energy and labor intensive and are expensive.
It is an object of this invention to provide a device and method for removing and recovering halohydrocarbon dry cleaning solvent from spent filters or residues which device and method are energy and labor efficient and relatively inexpensive to use and install.
It is a further object to provide a device and method which will reduce the solvent content of spent filters or residues to a level which will permit their disposal as nonhazardous substances--which level is often 1% solvent or less.